1. Field of the Invention
The present invention relates to a semiconductor device having a functional portion with the characteristics being easily changed by an as-manufactured error, and a method of manufacturing the semiconductor device.
2. Description of the Related Art
In a Vertical Cavity Surface Emitting Laser (VCSEL), a pair of multilayer film reflectors is formed on a substrate, and an active layer as a light emitting region is provided between the pair of multilayer film reflectors. In one of the multilayer film reflectors, in order to improve efficiency of current injection into the active layer and lower the threshold value current, a current confinement layer having a structure that a current injection region is confined is provided. Further, a post-shaped mesa is formed in the semiconductor layers. An upper electrode is provided on the upper face side of the mesa. A lower electrode is provided on the rear face side of the substrate. An aperture for emitting laser light is provided in the upper electrode. In the VCSEL, a current injected from the upper electrode and the lower electrode is confined by the current confinement layer, and then is injected into the active layer, where light is emitted. While the light is repeatedly reflected by the pair of multilayer film reflectors, the light is emitted from the aperture as laser light.
The foregoing current confinement layer is generally formed by oxidizing an AlAs layer from the side face of the mesa. In the past, for example, the current confinement layer has been formed by controlling the oxidation confinement diameter (diameter of the current injection region as a non-oxidation region) by oxidation time. Otherwise, as described in Japanese Unexamined Patent Application Publication No. 2001-210908, the current confinement layer has been formed by forming a mesa for monitoring in one wafer, and controlling the oxidation confinement diameter by reflectance change corresponding to the oxidation area in the lamination face of the AlAs layer included in the mesa.
However, the oxidation rate of the AlAs layer largely depends on the thickness of the AlAs layer, the impurity concentration or the like as well as the substrate temperature and the supply flow rate of reactive gas. Therefore, in general, reproducibility of the oxidation confinement diameter is poor, and the oxidation confinement diameter varies even in one wafer face. In the result, even when the foregoing method is used, the error of the oxidation confinement diameter resulting from such poor reproducibility and variation of the oxidation confinement diameter in the wafer face is often larger than the precision necessary for the oxidation confinement diameter (for example, ±0.5 μm or more), leading to lowering of the number of VCSELs (yield) obtained from one wafer.